The Global System for Mobile Communications (GSM) is one or more networks that execute cell phone calls. GSM networks include various network elements that are used to complete a call. For example, GSM networks can include a Home Location Register (HLR), Mobile Switching Center (MSC), and Gateway Mobile Switching Center (GMSC). In addition to providing call connections, mobile provider networks provide Intelligent Network (IN) services to enhance service provided to customers. Video downloads, music downloads, prepaid service, automated call forwarding, and ring-back tone services are a few of such enhanced services. Enhanced services can be implemented using Customized Applications for Mobile Network Enhanced Logic (CAMEL) protocol.
CAMEL protocol is a set of standards defined by European Telecommunication Standardization Institute (ETSI). Subsequently, Third Generation Partnership Project (3GPP) defined upgrades to the CAMEL protocol. CAMEL protocol enables service providers to continue to service their subscribers with enhanced services even when a subscriber is roaming outside of their home network.
When a call is made to a subscriber's equipment (commonly referred to as user equipment (UE)), a GMSC establishes CAMEL Application Protocol (CAP) dialogues to supply services to the UE. Simultaneously, an MSC that is connected to the GMSC and servicing the UE pages the UE. When the UE moves from a location that is covered by the MSC to a location that is covered by a second MSC, the UE sends out a location update to the second MSC. Location update is described in 3GPP TS 23.018.
If a first MSC receives a call to a UE while the UE is moving from a geographic location served by the first MSC to a geographic location served by the second MSC, the first MSC sends a paging message to the UE at the same time that the UE is in the process of a location update. Thus, the UE does not respond to the paging message and the first MSC can not establish the call. Mobile Terminating Roaming Retry Call (MTRR) has been implemented to address this problem. If MTRR is implemented on the GMSC, when the UE transmits a location update, the HLR transmits a cancel location message to the first MSC. The first MSC aborts paging the UE and transmits a Resume Call Handling (RCH) message to the GMSC. The RCH message indicates whether MTRR is requested for this call.
When the GMSC receives a RCH message that indicates MTRR is requested, it terminates all ongoing CAP dialogues. After the location update is complete the GMSC reestablishes the CAP dialogues. Terminating and reestablishing the CAP dialogues can create an interruption in a subscriber's service. For example, if a caller's tune is being played to the calling party by a CAP dialogue, when the CAP dialogue is terminated the tune is stopped. When the CAP dialogue is terminated, the caller will no longer hear the tune and may hang up due to the lack of audio. Therefore, it is desirable to selectively terminate CAP dialogues, rather than terminate all CAP dialogues upon receipt of a RCH message by the GMSC when MTRR is enabled.